A strange thing happened the other day, i was trying to get a group for the daily heroic. A pally and Rogue invited me to join them, on joining them saw i had only 13k health gave me some abuse and left the group. I have never had any problems tanking any heroics or kara and OTd in gruul and The Eye.
Is my health too low? Should i switch avoidance for stamina?
Can't get your armory to work, but 13k hp does sound slightly low for that progression. I am a tauren so have a small advantage, but I believe I was at 15k hp when I started doing kara. Unfortunately most pug heroics look for quick, wipeless runs, so a tank with low hp will frighten the idiots too stupid or lazy to give a tank a chance. Your raid members will hopefully know you and value your gear and tanking style, but pugs create their own set of rules.